The goal of the project is to develop the next generation CT detector modules for x-ray CT scanners based on high-throughput photon-counting cadmium zinc telluride (CZT) detectors combined with CMOS readout arrays. This new technology will deliver significant improvements in diagnostic capabilities. We will develop a novel detector module which adds several new important features compared with the basic principles of technology currently used by all major CT manufacturers. The currently commercially-available CT systems typically use a detector having silicon (Si) (p-n junction) photodiodes that are optically coupled to a scintillator which is operated in a current-integrating mode where the signals generated from the x-rays are integrated in each pixel over a time before the integrated charge is read out. The use of these current-mode detectors results in generally poorer image quality than could be achieved by using the technology proposed in the product presented here. Instead of integrating the x-ray current over a time, photon counting is used to measure and count each x-ray individually over a similar time. By doing this, the following additional features can be obtained: counting (and analysis) of each individual x-ray, binning events according to x-ray energies, and spectroscopic x-ray imaging capabilities. These new features lead to: potentially significantly reduced x-ray dose to the patient, compositional analysis of tissue through spectroscopic x-ray imaging, and potentially significant improvement in overall image quality. In Phase I we will develop and test a drift structure for each individual pixel element to greatly increase the count-rat capability of the detector system, a critical characteristic due to the large x-ray flux incident on x-ray CT detectors. We will choose an optimal structure by performing simulations and then measuring the actual performance of the structure on high-quality CZT detectors. The Phase I work will reduce the risk for the successful completion of Phase II, where we will construct the detector module prototype which will consist of individual detector modules (tiles) arranged in a (one- or two- dimensional) array so as to form the entire detector. Each detector module (tile) constitutes a pixillated semiconductor detector that allows for direct conversion of the x-rays. In addition it uses highly advanced next generation integrated circuits in order to produce digital x-ray CT images where each individual x-ray is counted and analyzed. [unreadable] [unreadable] [unreadable]